Hard disk drives are used in almost all computer system operations. In fact, most computing systems are not operational without some type of hard disk drive to store the most basic computing information such as the boot operation, the operating system, the applications, and the like. In general, the hard disk drive is a device which may or may not be removable, but without which the computing system will generally not operate.
The basic hard disk drive model was established approximately 50 years ago and resembles a phonograph. That is, the hard drive model includes a storage disk or hard disk that spins at a standard rotational speed. An actuator arm with a suspended slider is utilized to reach out over the disk. The arm carries a head assembly that has a magnetic read/write transducer or head for reading/writing information to or from a location on the disk. The complete head assembly, e.g., the suspension and head, is called a head gimbal assembly (HGA).
In operation, the hard disk is rotated at a set speed via a spindle motor assembly having a central drive hub. Additionally, there are tracks evenly spaced at known intervals across the disk. When a request for a read of a specific portion or track is received, the hard disk aligns the read-write heads, via the head gimbal assembly, over the specific track location and the read head reads the information from the disk. In the same manner, when a request for a write of a specific portion or track is received, the hard disk aligns the read-write heads, over the specific track location and the head writes the information to the disk.
Over the years, the disk and the head have undergone great reductions in their size. Much of the refinement has been driven by consumer demand for smaller and more portable hard drives such as those used in personal digital assistants (PDAs), MP3 players, and the like. For example, the original hard disk drive had a disk diameter of 24 inches. Modern hard disk drives are much smaller and include disk diameters of less than 2.5 inches (micro drives are significantly smaller than that).
Advances in magnetic recording are also primary reasons for the reduction in size. For example, advances have led to storage capacities in the range of 120 gigabytes (GB) per square inch of disk real estate. Thus, multi-hard disk drives have capacities in the range hundreds of gigabytes. In the present environment, even small improvements in storage techniques can produce large absolute changes in total capacity. For example, a 4% improvement in the capacity of a 250 GB hard disk drive results in an extra 10 GB of additional storage capacity. This is more than the original capacity of hard disk drives offered in the late 1990's.
Presently, the read-write head position geometry on the slider has evolved to meet the needs for both the increased magnetic density and better servo tracking methods. For example, current methods for obtaining timing information for a read-write operation make use of the previously written track, thereby avoiding having to use a clock track. This improvement is important and is not to be abandoned. However, in order to utilize the previously written track information the read-write head geometry is formed in an offset manner to allow the read-write head to read the previous track information across the entire disk surface area. As a result of the current read-write head offset geometry, valuable amounts of disk surface real estate are wasted (sacrificed) in the servo track read-write activity.
For example, as shown in Prior Art FIG. 1, when the head gimbal assembly (HGA) 102A is reading at the inside diameter 111 location, the read-write head is oriented in a different direction than when the HGA 102B is oriented on the outside diameter 121 of the disk 115.
Prior Art FIG. 2 provides a view of the bottom of the head 211 shows the different orientation of the head 211 as shown in inside diameter 111 versus the outside diameter 121. In general, Prior Art FIG. 2 depicts the alignment of the read-write head as previously mentioned. During the writing of the servo information track the read head 204 is required to read the previously writing servo track information 231 and use the timing information to write the next servo track information 233 at the outermost diameter 121 of the disk 115. The separation between the read head 204 and the write head 208 is determined by the outermost diameter 121 and the requirement for the read head 204 to read the previous servo track information 231 and the requirement for the write head 208 to write the last servo track information 203 at the outermost diameter of the disk 121
Referring now to Prior Art FIG. 3, a diagram of the offset read-write elements on the head 211 illustrating the loss of disk surface real estate is shown. In operation, in order for the write elements 208 to begin writing, the read element 204 must stop reading. This step creates a costly and undesirable unused space 308 where nothing can be written because the read element 204 has not yet stopped reading. In addition, this wasted space grows as the HGA moves from the inside diameter 111 to the outside diameter 121 due to the geometry of the read-write elements.